The present invention relates to plasma reactors for the fabrication of integrated circuits (IC's). More particularly, the present invention relates to methods and apparatus for coupling ceramic and metallic reactor parts of plasma reactors to reduce damage caused by thermal expansion.
In semiconductor IC fabrication, plasma etch chambers used for IC fabrication were often designed from metallic materials, such as aluminum. These metal etch chambers caused slight amounts of metal contamination within the chamber environment, but this contamination was tolerated because it did not adversely effect larger architecture IC fabrication. However, as semiconductor features have diminished in size, for example from 0.5 microns to 0.13 microns, with a corresponding increase in complexity, the processes used to etch the features into the semiconductor devices have become much more sensitive to their environments and, more particularly, to metallic contaminants.
As a result, etch chamber materials, such as their state of cleanliness, temperature, and electrical state, must be more stringently controlled than in the past. Process requirements often require high-purity, metal free ceramics with tightly controlled temperature profiles to form the environment in which wafers are etched. In addition, in many cases the ceramics must be electrically conductive to provide low impedance ground paths for the plasma.
Since ceramics are brittle materials, with coefficients of thermal expansion much different than metal components of the chamber, the interfacing of the ceramic components to metal components is problematic. Critical interfaces are present in the etch chamber in which ceramic liner parts are attached to metal components which heat them and maintain their temperature within closely controlled limits. Because these interfaces occur between metal and ceramic components, loading must be controlled and not excessive, or damage such as fracturing or breakage may occur to the ceramics. These requirements dictate careful torquing of chamber bolts to achieve pressure in the desired range. Since assembly time is very important to the chip manufacturer, and since errors in the torquing of the bolts result in costly damage to ceramics, it is important to assemble the joints quickly and accurately.
In addition, since heat is transmitted by conduction across the metal and ceramic interface, the pressure over the entire surface of the interface should be maintained above a threshold value for the heat to be transmitted efficiently. However, the thermal expansion of the supporting metal components is far greater than that of the ceramics, creating a situation in which the ceramics are fractured by expansion loads when supported tightly enough to provide a good thermal conductance across the interface.
In view of the forgoing, what is needed are improved methods and apparatuses for interfacing ceramics and metals within a plasma chamber to reduce damage caused to ceramics by the thermal expansion of the supporting metal components. Further, there is a need for methods and apparatuses that allow assembly of plasma reaction chambers quickly and accurately to reduce down time for the reactor and increase reactor yield.